1. Field of the Invention
The present invention is directed to a cathode ray tube having an internal magnetic shield for minimizing the effects of external magnetic fields.
2. DESCRIPTION OF THE PRIOR ART
In a cathode ray tube, the phosphor screen must be designed with a tolerance so as to prevent the occurrence of color misregistration even when there is an electron beam mis-landing on the phosphor screen caused by an external magnetic field, such as the earth's terrestrial magnetic field. As the amount which the electron beam mis-lands decreases, the necessary amount of tolerance becomes smaller also and a cathode ray tube of high quality can be manufactured. For this reason, various structures of magnetic shield for use in cathode ray tubes have been proposed in order to reduce the amount of mis-landing of the electron beam due to terrestrial magnetism.
FIG. 1 illustrates an example of a conventional internal magnetic shield used in a cathode ray tube. As illustrated in FIG. 1, this internal magnetic shield 1 is formed of a magnetic plate 3 having a trapezoidal shape along the longer side of a panel 2 of the cathode ray tube and a magnetic plate 5 having a V-shaped groove 4 located along the short side of the panel 2.
A variant of such a magnetic shield has also been proposed such that a magnetic plate of the inner magnetic shield is formed as a hollow double structure in order to improve the shielding effect. This type of structure is disclosed in Japanese Laid-Open Utility Model Application No. 52-42055. This type of magnetic shield, however, does not improve the magnetic shielding effects efficiently since it does not minimize the electron beam mis-landing.